1. Field of the Invention
The present invention relates to an optical pickup apparatus for emitting a plurality of laser beams at different wavelengths to read information from a plurality of different recording media, and a laser diode chip for the optical pickup apparatus.
2. Description of Related Art
Generally, a semiconductor laser device is used as a light source for an optical pickup apparatus for reproducing optical discs such as a CD and a DVD.
For favorably reproducing the discs, semiconductor laser devices for emitting light at different wavelengths and objective lenses having different numerical apertures (NA) are required for reproducing a CD and for reproducing a DVD. For example, the reproduction of a DVD requires the wavelength of 650 nm and NA of 0.6, while the reproduction of a CD requires the wavelength of 780 nm and NA of 0.45.
For enabling a single player to reproduce different types of discs such as a CD and a DVD, an optical pickup apparatus which incorporates a light source for emitting light at two wavelengths 650 nm and 780 nm has been taken into consideration. FIG. 1 illustrates an example of the optical pickup apparatus.
The optical pickup apparatus illustrated in FIG. 1 comprises a laser device 1 for emitting a laser beam at wavelength of 650 nm; a laser device 2 for emitting a laser beam at wavelength of 780 mm; a combiner prism 4; a half mirror 4; a collimator lens 5; and an objective lens 6. These components are arranged in sequence. Further, a cylindrical lens (not shown) and a photodetector 7 are arranged on another optical axis which branches off the half mirror 4. In this configuration, an optical system from the combiner prism 3 to a disc 8 is shared by a CD and a DVD, so that in either case, light emitted from either of the laser devices is led to the disk 8 along the optical axis Y after it passes through the combiner prism 3. The objective lens 6 used herein is a bifocal lens which can provide focal points different from each other in accordance with the two wavelengths. This can limit spherical aberration caused by a difference in the thickness of surface substrate between a CD and a DVD.
However, the foregoing configuration requires a large number of parts including the combiner prism and is therefore expensive. In addition, the optical pickup apparatus requires alignment of the two laser devices with the combiner prism, causing a complicated configuration and difficult adjustments for the alignment.
In view of the problem mentioned above, it is an object of the present invention to provide an optical pickup apparatus which is capable of simplifying the configuration for using a plurality of laser beams at different wavelengths to reduce the size, and a laser diode chip for use therewith.
An optical pickup apparatus according to the present invention includes a light emitter having a first light emitting section for emitting a first laser beam, and a second light emitting section for emitting a second laser beam having a wavelength different from that of the first laser beam, for selectively emitting a laser beam from one of the first and second light emitting sections, and an optical system formed with a irradiation light path for leading the laser beam emitted from the light emitter to a recording medium, and a reflection light path for leading the laser beam reflected by the recording medium to a light detector, wherein the irradiation light path includes a first optical axis correcting element for allowing the first laser beam to pass therethrough and for diffracting the second laser beam to generate diffracted light having an optical path substantially matching an optical path of the first laser beam, and the first optical axis correcting element being arranged at a position at which the center of a light intensity distribution of the first laser beam incident thereto matches the center of a light intensity distribution of the second laser beam incident thereto.
A laser diode chip for an optical pickup apparatus according to the present invention has at least two light emitting sections for emitting laser beams at different wavelengths from each other, wherein the at least two light emitting sections are arranged such that the laser beams are emitted in directions different from each other.
Also, an optical pickup apparatus according to the present invention includes a light emitter having a first light emitting section for emitting a first laser beam, and a second light emitting section for emitting a second laser beam having a wavelength different from that of the first laser beam, for selectively emitting a laser beam from one of the first and second light emitting sections, and an optical system formed with a irradiation light path for leading the laser beam emitted from the light emitter to a recording medium, and a reflection light pat for leading the laser beam reflected by the recording medium to a light detector, wherein the irradiation light path includes an optical axis correcting element for allowing the first laser beam to pass therethrough and for diffracting the second laser beam to generate diffracted light which is directed to substantially the same direction a the 0-order light of the first laser beam, and the optical axis correcting element is configured to diffract the second laser beam such that the centers of gravity of the light amount distributions of spots of the first and second laser beams match on a light receiving surface of the photodetector.